TRACEROUTE(8)                 Traceroute For Linux                 TRACEROUTE(8)

       traceroute - print the route packets trace to network host

       traceroute [-46dFITUnreAV] [-f first_ttl] [-g gate,...]
               [-i device] [-m max_ttl] [-p port] [-s src_addr]
               [-q nqueries] [-N squeries] [-t tos]
               [-l flow_label] [-w waittimes] [-z sendwait] [-UL] [-D]
               [-P proto] [--sport=port] [-M method] [-O mod_options]
               [--mtu] [--back]
               host [packet_len]
       traceroute6  [options]

       traceroute tracks the route packets taken from an IP network on their way
       to a given host. It utilizes the IP protocol's time to live (TTL) field
       and attempts to elicit an ICMP TIME_EXCEEDED response from each gateway
       along the path to the host.

       traceroute6 is equivalent to traceroute -6

       The only required parameter is the name or IP address of the destination
       host .  The optional packet_len`gth is the total size of the probing
       packet (default 60 bytes for IPv4 and 80 for IPv6). The specified size
       can be ignored in some situations or increased up to a minimal value.

       This program attempts to trace the route an IP packet would follow to
       some internet host by launching probe packets with a small ttl (time to
       live) then listening for an ICMP "time exceeded" reply from a gateway.
       We start our probes with a ttl of one and increase by one until we get an
       ICMP "port unreachable" (or TCP reset), which means we got to the "host",
       or hit a max (which defaults to 30 hops). Three probes (by default) are
       sent at each ttl setting and a line is printed showing the ttl, address
       of the gateway and round trip time of each probe. The address can be
       followed by additional information when requested. If the probe answers
       come from different gateways, the address of each responding system will
       be printed.  If there is no response within a certain timeout, an "*"
       (asterisk) is printed for that probe.

       After the trip time, some additional annotation can be printed: !H, !N,
       or !P (host, network or protocol unreachable), !S (source route failed),
       !F (fragmentation needed), !X (communication administratively
       prohibited), !V (host precedence violation), !C (precedence cutoff in
       effect), or !<num> (ICMP unreachable code <num>).  If almost all the
       probes result in some kind of unreachable, traceroute will give up and

       We don't want the destination host to process the UDP probe packets, so
       the destination port is set to an unlikely value (you can change it with
       the -p flag). There is no such a problem for ICMP or TCP tracerouting
       (for TCP we use half-open technique, which prevents our probes to be seen
       by applications on the destination host).

       In the modern network environment the traditional traceroute methods can
       not be always applicable, because of widespread use of firewalls.  Such
       firewalls filter the "unlikely" UDP ports, or even ICMP echoes.  To solve
       this, some additional tracerouting methods are implemented (including
       tcp), see LIST OF AVAILABLE METHODS below. Such methods try to use
       particular protocol and source/destination port, in order to bypass
       firewalls (to be seen by firewalls just as a start of allowed type of a
       network session).

       --help Print help info and exit.

       -4, -6 Explicitly force IPv4 or IPv6 tracerouting. By default, the
              program will try to resolve the name given, and choose the
              appropriate protocol automatically. If resolving a host name
              returns both IPv4 and IPv6 addresses, traceroute will use IPv4.

       -I, --icmp
              Use ICMP ECHO for probes

       -T, --tcp
              Use TCP SYN for probes

       -d, --debug
              Enable socket level debugging (when the Linux kernel supports it)

       -F, --dont-fragment
              Do not fragment probe packets. (For IPv4 it also sets DF bit,
              which tells intermediate routers not to fragment remotely as

              Varying the size of the probing packet by the packet_len command
              line parameter, you can manually obtain information about the MTU
              of individual network hops. The --mtu option (see below) tries to
              do this automatically.

              Note, that non-fragmented features (like -F or --mtu) work
              properly since the Linux kernel 2.6.22 only.  Before that version,
              IPv6 was always fragmented, IPv4 could use the once the discovered
              final mtu only (from the route cache), which can be less than the
              actual mtu of a device.

       -f first_ttl, --first=first_ttl
              Specifies with what TTL to start. Defaults to 1.

       -g gateway, --gateway=gateway
              Tells traceroute to add an IP source routing option to the
              outgoing packet that tells the network to route the packet through
              the specified gateway (most routers have disabled source routing
              for security reasons).  In general, several gateway's is allowed
              (comma separated). For IPv6, the form of num,addr,addr...  is
              allowed, where num is a route header type (default is type 2).
              Note the type 0 route header is now deprecated (rfc5095).

       -i interface, --interface=interface
              Specifies the interface through which traceroute should send
              packets. By default, the interface is selected according to the
              routing table.

       -m max_ttl, --max-hops=max_ttl
              Specifies the maximum number of hops (max time-to-live value)
              traceroute will probe. The default is 30.

       -N squeries, --sim-queries=squeries
              Specifies the number of probe packets sent out simultaneously.
              Sending several probes concurrently can speed up traceroute
              considerably. The default value is 16.
              Note that some routers and hosts can use ICMP rate throttling. In
              such a situation specifying too large number can lead to loss of
              some responses.

       -n     Do not try to map IP addresses to host names when displaying them.

       -p port, --port=port
              For UDP tracing, specifies the destination port base traceroute
              will use (the destination port number will be incremented by each
              For ICMP tracing, specifies the initial ICMP sequence value
              (incremented by each probe too).
              For TCP and others specifies just the (constant) destination port
              to connect.

       -t tos, --tos=tos
              For IPv4, set the Type of Service (TOS) and Precedence value.
              Useful values are 16 (low delay) and 8 (high throughput). Note
              that in order to use some TOS precedence values, you have to be
              super user.
              For IPv6, set the Traffic Control value.

       -l flow_label, --flowlabel=flow_label
              Use specified flow_label for IPv6 packets.

       -w max[,here,near], --wait=max[,here,near]
              Determines how long to wait for a response to a probe.

              There are three (in general) float values separated by a comma (or
              a slash).  Max specifies the maximum time (in seconds, default
              5.0) to wait, in any case.

              Traditional traceroute implementation always waited whole max
              seconds for any probe. But if we already have some replies from
              the same hop, or even from some next hop, we can use the round
              trip time of such a reply as a hint to determine the actual
              reasonable amount of time to wait.

              The optional here (default 3.0) specifies a factor to multiply the
              round trip time of an already received response from the same hop.
              The resulting value is used as a timeout for the probe, instead of
              (but no more than) max.  The optional near (default 10.0)
              specifies a similar factor for a response from some next hop.
              (The time of the first found result is used in both cases).

              First, we look for the same hop (of the probe which will be
              printed first from now).  If nothing found, then look for some
              next hop. If nothing found, use max.  If here and/or near have
              zero values, the corresponding computation is skipped.
              Here and near are always set to zero if only max is specified (for
              compatibility with previous versions).

       -q nqueries, --queries=nqueries
              Sets the number of probe packets per hop. The default is 3.

       -r     Bypass the normal routing tables and send directly to a host on an
              attached network.  If the host is not on a directly-attached
              network, an error is returned.  This option can be used to ping a
              local host through an interface that has no route through it.

       -s source_addr, --source=source_addr
              Chooses an alternative source address. Note that you must select
              the address of one of the interfaces.  By default, the address of
              the outgoing interface is used.

       -z sendwait, --sendwait=sendwait
              Minimal time interval between probes (default 0).  If the value is
              more than 10, then it specifies a number in milliseconds, else it
              is a number of seconds (float point values allowed too).  Useful
              when some routers use rate-limit for ICMP messages.

       -e, --extensions
              Show ICMP extensions (rfc4884). The general form is CLASS/TYPE:
              followed by a hexadecimal dump.  The MPLS (rfc4950) is shown
              parsed, in a form: MPLS:L=label,E=exp_use,S=stack_bottom,T=TTL
              (more objects separated by / ).

       -A, --as-path-lookups
              Perform AS path lookups in routing registries and print results
              directly after the corresponding addresses.

       -V, --version
              Print the version and exit.

       There are additional options intended for advanced usage (such as
       alternate trace methods etc.):

              Chooses the source port to use. Implies -N 1 -w 5 .  Normally
              source ports (if applicable) are chosen by the system.

              Set the firewall mark for outgoing packets (since the Linux kernel

       -M method, --module=name
              Use specified method for traceroute operations. Default
              traditional udp method has name default, icmp (-I) and tcp (-T)
              have names icmp and tcp respectively.
              Method-specific options can be passed by -O .  Most methods have
              their simple shortcuts, (-I means -M icmp, etc).

       -O option, --options=options
              Specifies some method-specific option. Several options are
              separated by comma (or use several -O on cmdline).  Each method
              may have its own specific options, or many not have them at all.
              To print information about available options, use -O help.

       -U, --udp
              Use UDP to particular destination port for tracerouting (instead
              of increasing the port per each probe). Default port is 53 (dns).

       -UL    Use UDPLITE for tracerouting (default port is 53).

       -D, --dccp
              Use DCCP Requests for probes.

       -P protocol, --protocol=protocol
              Use raw packet of specified protocol for tracerouting. Default
              protocol is 253 (rfc3692).

       --mtu  Discover MTU along the path being traced. Implies -F -N 1.  New
              mtu is printed once in a form of F=NUM at the first probe of a hop
              which requires such mtu to be reached. (Actually, the correspond
              "frag needed" icmp message normally is sent by the previous hop).

              Note, that some routers might cache once the seen information on a
              fragmentation. Thus you can receive the final mtu from a closer
              hop.  Try to specify an unusual tos by -t , this can help for one
              attempt (then it can be cached there as well).
              See -F option for more info.

       --back Print the number of backward hops when it seems different with the
              forward direction. This number is guessed in assumption that
              remote hops send reply packets with initial ttl set to either 64,
              or 128 or 255 (which seems a common practice). It is printed as a
              negate value in a form of '-NUM' .

       In general, a particular traceroute method may have to be chosen by
       -M name, but most of the methods have their simple cmdline switches (you
       can see them after the method name, if present).

       The traditional, ancient method of tracerouting. Used by default.

       Probe packets are udp datagrams with so-called "unlikely" destination
       ports.  The "unlikely" port of the first probe is 33434, then for each
       next probe it is incremented by one. Since the ports are expected to be
       unused, the destination host normally returns "icmp unreach port" as a
       final response.  (Nobody knows what happens when some application listens
       for such ports, though).

       This method is allowed for unprivileged users.

   icmp       -I
       Most usual method for now, which uses icmp echo packets for probes.
       If you can ping(8) the destination host, icmp tracerouting is applicable
       as well.

       This method may be allowed for unprivileged users since the kernel 3.0
       (IPv4, for IPv6 since 3.11), which supports new dgram icmp (or "ping")
       sockets. To allow such sockets, sysadmin should provide
       net/ipv4/ping_group_range sysctl range to match any group of the user.

       raw    Use only raw sockets (the traditional way).
              This way is tried first by default (for compatibility reasons),
              then new dgram icmp sockets as fallback.

       dgram  Use only dgram icmp sockets.

   tcp        -T
       Well-known modern method, intended to bypass firewalls.
       Uses the constant destination port (default is 80, http).

       If some filters are present in the network path, then most probably any
       "unlikely" udp ports (as for default method) or even icmp echoes (as for
       icmp) are filtered, and whole tracerouting will just stop at such a
       firewall.  To bypass a network filter, we have to use only allowed
       protocol/port combinations. If we trace for some, say, mailserver, then
       more likely -T -p 25 can reach it, even when -I can not.

       This method uses well-known "half-open technique", which prevents
       applications on the destination host from seeing our probes at all.
       Normally, a tcp syn is sent. For non-listened ports we receive tcp reset,
       and all is done. For active listening ports we receive tcp syn+ack, but
       answer by tcp reset (instead of expected tcp ack), this way the remote
       tcp session is dropped even without the application ever taking notice.

       There is a couple of options for tcp method:

              Sets specified tcp flags for probe packet, in any combination.

              Sets the flags field in the tcp header exactly to num.

       ecn    Send syn packet with tcp flags ECE and CWR (for Explicit
              Congestion Notification, rfc3168).

              Use the corresponding tcp header option in the outgoing probe

       sysctl Use current sysctl (/proc/sys/net/*) setting for the tcp header
              options above and ecn.  Always set by default, if nothing else

              Use value of num for maxseg tcp header option (when syn).

       info   Print tcp flags of final tcp replies when the target host is
              reached.  Allows to determine whether an application listens the
              port and other useful things.

       Default options is syn,sysctl.

       An initial implementation of tcp method, simple using connect(2) call,
       which does full tcp session opening. Not recommended for normal use,
       because a destination application is always affected (and can be

   udp        -U
       Use udp datagram with constant destination port (default 53, dns).
       Intended to bypass firewall as well.

       Note, that unlike in tcp method, the correspond application on the
       destination host always receive our probes (with random data), and most
       can easily be confused by them. Most cases it will not respond to our
       packets though, so we will never see the final hop in the trace.
       (Fortunately, it seems that at least dns servers replies with something

       This method is allowed for unprivileged users.

   udplite    -UL
       Use udplite datagram for probes (with constant destination port, default

       This method is allowed for unprivileged users.

              Set udplite send coverage to num.

   dccp    -D
       Use DCCP Request packets for probes (rfc4340).

       This method uses the same "half-open technique" as used for TCP.  The
       default destination port is 33434.


              Set DCCP service code to num (default is 1885957735).

   raw        -P proto
       Send raw packet of protocol proto.
       No protocol-specific headers are used, just IP header only.
       Implies -N 1 -w 5 .

              Use IP protocol proto (default 253).

       To speed up work, normally several probes are sent simultaneously.  On
       the other hand, it creates a "storm of packages", especially in the reply
       direction. Routers can throttle the rate of icmp responses, and some of
       replies can be lost. To avoid this, decrease the number of simultaneous
       probes, or even set it to 1 (like in initial traceroute implementation),
       i.e.  -N 1

       The final (target) host can drop some of the simultaneous probes, and
       might even answer only the latest ones. It can lead to extra "looks like
       expired" hops near the final hop. We use a smart algorithm to auto-detect
       such a situation, but if it cannot help in your case, just use -N 1 too.

       For even greater stability you can slow down the program's work by -z
       option, for example use -z 0.5 for half-second pause between probes.

       To avoid an extra waiting, we use adaptive algorithm for timeouts (see -w
       option for more info). It can lead to premature expiry (especially when
       response times differ at times) and printing "*" instead of a time. In
       such a case, switch this algorithm off, by specifying -w with the desired
       timeout only (for example, -w 5).

       If some hops report nothing for every method, the last chance to obtain
       something is to use ping -R command (IPv4, and for nearest 8 hops only).

       ping(8), ping6(8), tcpdump(8), netstat(8)

Traceroute                       11 October 2006                   TRACEROUTE(8)